1. Field of the Invention
The present invention relates to a motor control device and a steering control device.
2. Description of the Related Art
Japanese Patent Application Publication No. 2015-80327 (JP 2015-80327 A), for example, discloses a motor control device that includes two control systems (control units or inverters) that supply drive electric power to a motor using external power sources as electric power sources. The motor control device also includes two electric power supply paths that connect between the two control systems and the external power sources, respectively. This increases the redundancy of the control system in the motor control device described in JP 2015-80327 A.
To increase the redundancy in a motor control device, it is also conceivable to increase the redundancy of the electric power source of drive electric power by connecting different external power sources to control systems. That is, different external power sources are independently connected to the motor control device, and the low potential sides of the different external power sources are connected to the control systems of the motor control device via power source grounds (so-called “frame grounds”) which are independent grounds, for example. In order to enable communication between the control systems, the low potential sides of the control systems are connected to each other via an internal ground (so-called “signal ground”) which is a common ground.
In the case where an abnormality such as a short circuit is caused in any of the power source grounds in the example described above, the control systems are connected to the remaining normal power source grounds through the internal ground. That is, the control system connected to the power source ground in which an abnormality is caused can operate normally through the remaining normal power source grounds. Therefore, in the case where the redundancy of the electric power source of drive electric power is increased, it is difficult to detect an abnormality in the power source grounds even if operation of the motor control device is monitored from the outside, which may lower the reliability of the motor control device.
Besides, the motor control device may be used as a steering control device for a vehicle when the motor control device is mounted on the vehicle which enables automated drive in which the travel direction of the vehicle is automatically varied. To increase the redundancy of the electric power source of drive electric power as in the example described above in such a steering control device, an abnormality in the power source ground may not be detected immediately, e.g. the timing to stop the automated drive function may be delayed, which may lower the reliability of the steering control device.